The present invention relates generally to improvements to the delivery of drugs, particularly to systems for subcutaneous injection/aspiration into a fluid filled space of the body. More specifically the invention provides a method and device to identify a fluid-filled tissue space of the body by stopping fluid flow based on a predetermined pressure measurement and resuming fluid flow once the pressure drops below a predetermined pressure measurement.
A regional anesthesia block of epidural tissue-space is understood to produce effective transient anesthesia of the lower extremities of the body. It can be effectively used for a vast number of invasive procedures of the body, including but not limited to child birth, prosthetic hip replacement and a variety of other surgical procedures where anesthesia below the waist is required. It can also be effectively used for treatment of chronic and acute pain including, for example, “back-pain,” ailments of the vertebrae and, compression of the accessory nerves of the spinal column. To achieve effective regional anesthesia and to block nerve transmission to the CNS an adequate volume of a local anesthetic solution must be deposited in close proximity to the spinal cord at a particular level of the vertebral column within the anatomic site known as the epidural “space.”
The epidural space is that part of the vertebral canal not occupied by the dura mater and its contents. It lies between the dura and the periosteum lining the inside of the vertebral canal. It extends from the foramen magnum to the sacral hiatus. The anterior and posterior nerve roots in their dural covering pass across the epidural space to unite in the intervertebral bodies, and the intravertebral discs. Laterally, the epidural space is bordered by the periosteum of the vertebral pedicles, and the intervertebral foramina. Posteriorly, the bordering structures are the periosteum of the anterior surface of the laminae, the articular processes and their connecting ligaments, the periosteum of the root of the spines, and the interlaminar spaces filled by the ligamentum flavum. The space contains venous plexuses and fatty tissue which is continuous with the fat in the paravertebral space.
The epidural fluid filled space (posterior epidural space) is a limited anatomic area with an irregular shape measuring in several square millimeters with respect to cross section of the vertebrae and spinal column. The fluid filled space is very narrow and is associated closely with the dura of the spinal column with the ligamentum flavum closely adjacent. The fluid filled space therefore has to be clearly identified when the bevel or point of the needle exits the ligamentum flavum, as the dura will be punctured if the needle continues to penetrate. The standard technique for locating the epidural fluid filled space employs the “loss-of-resistance” technique. This technique utilizes a low-friction syringe made of plastic or glass connected to an epidural Touhly needle (16 to 18 gauge).
The block can be performed with the patient either in the sitting or lateral decubitus position. The patient should be encouraged to adapt a curled up position, as this tends to open the spaces between the spinous processes and facilitates the identification of the intervertebral spaces. Epidural injections can be sited at any level along the lumbar and thoracic spine, enabling its use in procedures ranging from thoracic surgery to lower limb procedures.
The clinician palpates the vertebral column at the appropriate level of the vertebral column between vertebrae. Local anesthesia is placed within the superficial tissues rendering the tissues of the area to be locally anesthetized. The dermis is then punctured using the Touhly needle and the needle is advanced while the clinician simultaneously applies pressure on the plunger of the syringe. The pressure on the plunger will unintentionally result in an amount of fluid continuously exiting out of the needle within the tissues.
Insertion of the epidural needle continues and advances through the supraspinous ligament, with the needle pointing in a slightly cephalad direction. The needle is advanced into the interspinous ligament, which is encountered at a depth of 2-3 cm, until the subjective sensation of increased resistance is felt as the needle passes into the ligamentum flavum. The needle is further advanced until the subjective “feel” of resistance by the clinician results in a distinct “back-pressure” on the plunger. The clinician must subjectively differentiate the “back-pressure” or resistance encountered to identify the location of the anatomic structure of the ligamentum flavum. The epidural fluid filled space is entered by the tip of the needle after it passes through the ligamentum flavum.
A known deficiency of this technique is loss of fluid into the tissues when the tip of the needle is in the interspinous ligament as the tissues there are not particularly dense.
The movement of the Touhly needle from penetration of the dermis to identification of the ligamentum flavum can vary from greatly in depth depending on the patient's physical size. Overweight patients present a greater challenge, and with the morbidly obese patient it may not be a suitable technique because of the limitations of subjective nature of this technique. Age appears to be an additional complicating factor because of the challenge presented by the reduced size of the anatomy of the epidural tissue-space. Small children are often subject to the more dangerous procedure of general anesthesia as a result.
Unfortunately, if the epidural procedure is not performed properly additional fluid is injected within the tissues indiscriminately while trying to determine the location of the fluid-filled epidural space. The additional fluid released into these tissues can further complicate the identification of the fluid-filled space.
Additionally, if the Touhly needle moves once the epidural space has been located, either by removal of the syringe or inadvertent movement of the patient or doctor's hand, the needle can either be unknowingly moved outside the epidural tissue-space or at worst advanced into dura of the spinal cord producing what is termed a “wet-tap”, which can have a dangerous long-term consequences to the patient. Even if the epidural space was initially properly located, if the needle further advances during the injection of the anesthetic solution it may deposit a bolus of anesthetic solution into the spinal cord resulting in transient or permanent nerve damage.
Infusion pumps devices and systems are well known in the medical arts, for use in delivery or dispensing a prescribed medication to a patient. Several attempts have been made to adapt these devices for the administration of an epidural injection.
Prior art references are known which attempt to utilize a pressure transducer to measure the pressure within the syringe (see U.S. Pat. No. 5,295,967 to Rondelet et al.). A major deficiency of these systems is their inability to adjust the flow rate and/or pressure of the fluid to compensate for changes in resistance throughout the system.
U.S. Pat. No. 7,922,689 to Lechner discloses a device for locating an anatomic cavity that rely on an alarm (i.e. audible or visual warning signal) requiring the operator to manually modulate the drug delivery system during an injection procedure. This device requires the continuous flow of fluid to identify the epidural tissues similar to the “loss-of-resistance” manual syringe technique. In addition, it relies upon a relative audible change related a pressure drop to identify the epidural tissues. The device requires subjective interpretation of events to which the operator must respond. Furthermore, the device provides continuous injection fluid delivery and attempts to generate a sufficient pressure to do so via an automatic syringe pump device. The device does not, however, provide a means for automatically controlling the injection pressure of fluid delivery or for aspiration of drug delivery during use. Thus, the device of U.S. Pat. No. 7,922,689 maintains injection flow rate despite excess fluid pressure that may result in pain and/or tissue damage.
The concept of using pressure as a metric to perform a safe and effective epidural injection has been well documented in the medical literature. Pressure has been used to identify the epidural space and the importance of pressure within the epidural space has been described by a number of researchers over the years utilizing a variety of experimental set-ups. Usubiaga and co-workers discussed the relationship of pressure and the epidural space while performing an injection into the epidural space and tissues (Anesth. Analg., 46: 440-446, 1967). Husenmeyer and White described the lumbar epidural injection technique and relationship of pressure of during injection in pregnant patients (Br. J. Anaesth., 52:55-59, 1980). Other investigators, including Paul and Wildsmith (Br. J. Anaesth., 62:368-372, 1989) and Hirabayashi et al. (Br. J. Anaesth., 1990 65:508-513), also evaluated the relationships between pressure and the effects of resistance on the administration of an epidural injection. Lakshmi Vas and co-workers have extended these principles into the area of pediatric medicine (Pediatric. Anesth. 11:575-583, 2001). Lechner and co-workers described a system for manual manipulation epidural injections based on pressure feedback (Anesthesia, 57:768-772, 2002; Anesth. Analg. 96:1183-1187, 2002; Euro. J. Anaestheol. 21:694-699, 2004).
The invention herein described improves the reliability and safety of epidural injection administration by limiting the fluid required to identify the epidural space. It also improves upon prior techniques by providing a predetermined pressure limit and a predetermined resumption of fluid flow below said pressure limit. Additionally, audible and/or visual signal information is provided when the system resumes fluid flow thereby detecting needle entry into the fluid filled space of epidural region.
U.S. Pat. No. 6,200,289 to Hochman et al., co-invented by the inventor of the subject application and incorporated herein by reference, discloses an automatic injection device that includes a drive mechanism that causes a therapeutic fluid to flow from a cartridge supported by a cartridge holder, a tube and a handle with an injection needle. The drive mechanism is connected to an electric motor and a sensor positioned at the motor output that measures the force applied by the motor to the drive mechanism. This force is then used to determine an internal characteristic such as a force or internal pressure generated during the injection process. This characteristic is then used as a control parameter by a microprocessor or controller which generates corresponding commands to the drive mechanism. In a particularly advantageous embodiment, the characteristic is used to calculate an exit pressure at which fluid is ejected by the device through an elongated tube. The electric motor is then operated in such a manner that the exit pressure is maintained at a predetermined level to insure that a patient does not suffer pain and/or tissue damage.
Published patent application US2011/0120566 to Ohmi et al. is from the non-analogous field of non-biological fluid supply methods for semiconductor manufacturing, chemical industrial and medical industrial facilities. The reference is sited, however, for its teaching of discontinuous switching of fluid flow rate using a pressure type flow rate control device. The probing of anatomic space is not contemplated and the person skilled in the art of designing medial treatment apparatuses and methods would not look to this non-analogous art for guidance.
Published patent application US2011/0301500 to Maguire et al. discloses an automated vessel puncture device using three-dimensional near infrared imaging and a robotically driven needle to providing simultaneous real-time diagnostic assays. It teaches that venipuncture is the process of obtaining a sample of venous blood for purposes of performing various tests. Samples are obtained manually from a vein or organ that is close to the surface of the skin by trained personnel, but there are problems inherent with these processes. This reference uses infrared imaging and a robotically driven needle to address the problem but does not use fluid pressure values to help indication the presence of vein or organ. Although pressure is mentioned, this refers to mechanical pressure resisting the movement of the mechanically driven needle to avert injury to the patient, not to fluid pressure in the needle.
Also see published U.S. patent application US2006/0122555 to Hochman, incorporated herein by reference, which discloses an in-line fluid pressure sensor between a syringe and tubing connected to a needle for injecting the fluid.
Other patents that disclose the use of a mechanical biasing force (rather than a transducer) to locate and control the flow of a fluid are U.S. Pat. Nos. 8,197,443 and 8,137,312 for detection apparatuses and methods.
Also see U.S. Pat. No. 8,142,414 for methods of injecting fluids into joints using a handpiece assembly, U.S. Pat. No. 8,079,976 for an articular injection system and published patent application US2006/0122555 for a drug infusion device for neural axial and peripheral nerve tissue identification using exit pressure sensing.
Additional more recent work of Lechner is also disclosed in his patent applications US2012/0101410 for unit, assembly, device and method for testing a sensor means provided in a medical localization device and US2012/0022407 for device for locating a structure inside a body.
A need remains for an apparatus and method that can accurately guide the insertion of a needle into a fluid-filled anatomic space having a lower pressure than its surrounding tissues, such as the epidural space near the spine, the intra-articular space in joints, fluid filled vessels of the body, and which apparatus and method can control both injection of fluid into and aspiration of fluid from the epidural space, and which apparatus and method further address the need for maintaining a sterile field and sterile conditions.